The present invention relates generally to the field of electrical panel enclosures and, more particularly, to a purge and cooling system for use with an enclosure adapted to contain heat generating electrical components, such as frequency control devices and the like, wherein the purge system provides sufficient volumetric air flow to cool the components, and adapted for use in a hazardous and/or explosive environment.
Drilling rigs present a hazardous environment wherein natural gas and other gases from down hole may develop an explosive mixture in the area. The area immediately around the borehole is classified as a Class 1 area, with the highest likelihood of such a hazard. Another annular region, between 10 and 30 feet from the borehole, is classified as a Class 2 area, and the region beyond 30 feet from the borehole is not classified, since this region does not typically present a hazard due to gases from the well.
The National Electrical Manufacturers Association (NEMA) has established standards for electrical components which are adapted to be used in such hazardous areas, such electrical components including frequency control devices for motors operating on and around drilling rigs. For example, Class 1, Division 1, group D dictates standards for enclosures used where natural gas may be present. One aspect of the standard for such enclosures requires a positive pressure within the enclosure of at least 0.5xe2x80x3 H2O pressure. Unfortunately, most enclosures which satisfy this requirement do not provide adequate air flow to cool the heat generating electrical components within the enclosure because the air is stagnant or stationary. To overcome this drawback, many systems further include an air conditioning system to cool the components. Such air conditioning systems must themselves satisfy the enclosure criteria, since they are generally included in the same area. Also, the air conditioning systems require more power, and present a maintenance problem, just as any additional equipment would do.
Known systems which pressurize enclosures having heat generating equipment therein and cooled by air conditioning system suffer from another drawback. Such enclosures with contained air systems with supply from seawater laden air typically develop substantial condensation within the enclosure. This phenomenon can be particularly destructive to electrical components within the enclosure.
Thus, there remains a need for a system which can provide a positive pressure within an enclosure intended for a hazardous environment in order to satisfy NEMA standards, and yet cool the electrical components within the enclosure without the need for an air conditioning system. Such a system should also minimize or even eliminate the tendency of such enclosure cooling systems to develop condensation within the enclosure. The present invention is directed to solving these and other problems in the art.
The present invention addresses these and other drawbacks in the art by providing a purge system to develop a positive pressure in an electrical enclosure, with sufficient volumetric air flow to cool the electrical components.
The system includes an air inlet hose, with the input into the inlet hose positioned in an unclassified (i.e. safe) area. The inlet hose couples to the suction of an air blower, while the discharge of the air blower is inside the electrical enclosure, thereby providing the necessary positive pressure (purge) within the enclosure. The air blower may be positioned outside the enclosure or, alternatively in a presently preferred embodiment, the air blower may be mounted within the enclosure. The air discharged from the air blower strikes a baffle, which distributes the blowing air throughout the bottom of the enclosure. The distributed air is then preferably drawn into controller cabinets by dedicated cooling fans. A conduit system connects the controller cabinets to take the now heated air from the cabinets to a discharge outside the enclosure. The outlet of the conduit system may include a counter-weighted flapper valve to maintain the pressure within the enclosure.
The volumetric flow rate is preferably sufficient to maintain no more than about a 10xc2x0 F. temperature rise across the enclosure. Thus, if the components within the enclosure are rated at 130xc2x0 F., then adequate margin is provided to cool the components even with an ambient temperature above 110xc2x0 F. or even higher.
The system also includes a feature of a time delay between the time of actuating a start signal to the electrical components within the enclosure and the actual shutting of contactors to start the components. This time delay is for the air blower to get up to speed and pressurize the enclosure to purge pressure before energizing the frequency controllers, for example, in the enclosure.
It is therefore an object of the present invention to provide a system and a method of cooling heat-generating electrical components within an enclosure. It is another object of the invention to cool such electrical components without the need for an air conditioning system comprising a heat pump or compressor using a coolant. It is a further object of the invention to cool electrical components within an enclosure for use within a hazardous environment.
These and other objects and features of the invention will be apparent to those of skill in the art from a review of the following detailed description along with the accompanying drawings.